Well i actually built a Lugia Legend deck and surprisingly its working quite well!
The biggest problem, that DNA pointed out, is that against SPs, they will power spray you, and those hurt even more because the P-Powers in a Lugia deck are all "coming into play" powers, so you'd have to waste resources to pick Lugia/Dialga up again.
Anyways, besides that, its an extremely fun deck to play! I have a blast every time I played it. A good starter would be Sableye, because you can go get Bebe Searches early on to get your Lugia pieces. Also, some Unown Q's cant hurt because Sableye and Lugia both have only 1 retreat cost. Itll make things easier for Seeker too (Hunter is actually called Seeker
). But dont forget the super scoop ups too
The biggest part of this deck though, believe it or not, is Legend Box! (Thats right, it finally has a use!)
With Dialga PL #5, You can very easily put a KOed or a discarded full Lugia Legend on the top of your deck, and then use Legend Box for a guaranteed success. And the best part about Lugia is that after a successful Legend Box, you can still use his P-Power Ocean Grow. (because it says when it "comes into play", and not "played from hand"). So basically you power him up with as many Energies as possible and attack away while still adding 1 energy every turn. Remember, you only need to attack 6 times to win the game pretty much.
Another important point though is to make sure you have 2-3 cards like Flower Shop Lady, to stop yourself from decking out with all the Ocean Grows and Sages Training (great card to thin out your deck and get Energies or even a 2nd Lugia to discard pile). As a last resort, any extra Dialga's can put three cards back in your deck too.
Anyways, thats my experience with Lugia Legend, i think its really fun to play. I hope you go through with this deck!